Today, in the world of portable electronic devices provided with displays there is a trend towards color displays. This trend is also very much present in the world of mobile communications, where more and more customers demand portable communcation devices having such displays. Typically such displays are of transparent type being illuminated by a lighting system, typically by a backlighting system. Examples of displays are different types of LCDs (Liquid Crystal Displays).
The display should be bright with good contrast. However, the power consumption of the lighting system (typically the backlighting) is high, thereby limiting the time the display can be switched on (herein, the term “switched on” means illuminated) in a portable electronic device. Typically an LCD itself consumes about 0.5 mA in a so-called “standby-mode” and about 80 mA with backlight switched on. Of course, this consumes battery power, hence reducing operating time of the portable electronic device.
Therefore, prior art technology has tried to reduce this problem. One way is to provide a colour filter that has an reflector behind for reflective operation. Ambient light then passes the colour filter and is reflected back, once more passing the color filter. However, this solution implies that reflected light (ambient light) has to travel through the color filter. Moreover, the reflector also reduce the area of the coluor filter during transmission of light, typically from a backlighting system. Since a typical colour filter may absorb more than 70% of the light this is often not a most desirable solution. There are also purely transmissive displays, wherein light is only transmitted from backlighting. Such solutions could for instance be found in lap-tops. However, these solutions provides poor out-door performance, hence in strong sun-light it could be hard, or even impossible to see any information on the display. Therefore, often also this solution does not perform well in out door use.
In US-A1-2001/0045560 (Bijsma et al) there is disclosed partly covering reflective parts of electrodes in a transfiective display with color filters, whereby the color point is adjusted.
However, there still exists problems with prior art that have to be overcome, or at least reduced.